New study: microplastics in the atmosphere can influence formation of ice clouds

New research led by scientists from Penn State University reveals microplastics in the atmosphere can significantly impact climate and climate change, potentially altering precipitation patterns and weather forecasting. Published in the journal Environmental Science and Technology: Air, the study confirms that microplastic particles can influence the formation of ice in clouds, which may have far-reaching consequences for Earth's weather systems.

Microplastics, defined as plastic particles or fibers smaller than 5 millimeters, with some being microscopic, have been found in some of the most pristine places on Earth. These locations include the depths of the Mariana Trench, the summit of Mount Everest, the mountain clouds of Japan and China, Antarctic deep seas, and fresh Antarctic snow. Microplastics have also been identified in the human brain, the stomachs of sea turtles, the roots of plants, and even in human blood.

The study was conducted by atmospheric chemists who examine how different types of particles form ice when they come into contact with liquid water. Miriam Freedman, a professor of chemistry at Penn State University and the lead author of the paper, emphasized the significance of the findings. "Microplastics can affect precipitation patterns, weather forecasting, climate modeling, and even aircraft safety," she stated.

To investigate whether microplastic fragments could serve as nuclei for water droplets, the researchers used four of the most prevalent types of plastics found in the atmosphere: low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). Each type of plastic was tested both in a pristine state and after exposure to ultraviolet light, ozone, and acids—conditions that mimic the environmental aging processes that plastics undergo in the atmosphere.

The researchers suspended the microplastics in small water droplets and slowly cooled the droplets to observe when they froze. They found that microplastic particles can produce ice crystals at temperatures 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit) warmer than droplets without microplastics. For most of the plastics studied, 50% of the droplets were frozen by the time they cooled to minus 22 degrees Celsius (minus 8 degrees Fahrenheit). This suggests that microplastics could cause ice crystals to form at warmer temperatures, potentially increasing rain or snowfall.

The study also revealed that environmental chemical processes can change the ability of microplastics to form ice. Exposure to ultraviolet radiation, ozone, and acids tended to decrease ice nucleation activity on the microplastic particles, although the microplastics still nucleated ice. This indicates that ice nucleation is sensitive to small chemical changes on the surface of microplastic particles.

Clouds form when water vapor sticks to tiny floating particles, such as dust or biological particles like pollen or bacteria, and turns into liquid water droplets or ice crystals. The presence of microplastics introduces a new type of particle that can serve as nuclei for ice formation. Ice in clouds has important effects on weather and climate because most precipitation typically starts as ice particles.

Clouds affect weather and climate by reflecting incoming sunlight away from Earth's surface, which has a cooling effect, and by absorbing some radiation emitted from Earth's surface, which has a warming effect. The amount of liquid water relative to ice in clouds determines their warming or cooling effect. If microplastics increase the presence of ice particles in clouds compared with liquid water droplets, this shifting ratio could change clouds' effect on Earth's energy balance.

Freedman explained that the implications of this discovery are not entirely clear but suggest that microplastics are likely already impacting the climate. "If microplastics are influencing mixed-phase cloud formation, they are likely affecting climate, too, but it's extremely difficult to model their overall effect," she said. "Clouds generally cool the Earth by reflecting solar radiation, but some clouds at specific altitudes can have a warming effect by retaining energy emitted from the Earth," she noted. 

The consequences of microplastic pollution for human health and biodiversity are increasingly documented. In 2022, the world produced more than 505 million tons of plastic, yet each year, less than 10% of the plastics produced are recycled. The rest are dispersed in nature, contributing to the widespread presence of microplastics in the environment.

In 2022, the United Nations launched negotiations for the signing of an international treaty to combat plastic pollution. Before the negotiations conclude with a final meeting of the Intergovernmental Committee scheduled in Busan, South Korea, starting November 25, scientists are emphasizing the urgent need to address the pervasive issue of microplastics and their impact on climate and environmental systems.

Sources: Live Science, Wired, PBS, Futura Sciences

This article was written in collaboration with generative AI company Alchemiq